Red Devils boss David Moyes is keen to sign a powerful central midfielder before the start of next season and Carvalho, who has been compared to former Arsenal enforcer Patrick Vieira, could be the ideal candidate.

According to The Metro, United have been tracking the 21-year-old for a long time and sent scouts to watch him during Sporting's 0-0 draw with Academica on Sunday.

Angola-born Carvalho is a full Portugal international, having made his senior international debut in November's 3-2 win over Sweden in World Cup qualifying.